Re: [PATCH v3 2/4] ASoC: fsl_asrc_m2m: Add option to start ASRC before DMA device for M2M

Frank Li
2026-02-03T17:54:21Z

On Tue, Feb 03, 2026 at 11:13:43AM +0800, Shengjiu Wang wrote:
> There is a limitation on i.MX952 that dma request is not cleared at the
> end of conversion with dma slave mode. Which causes sample is dropped
> from the input fifo on the second time if dma is triggered before the
> client device and EDMA may copy wrong data from output fifo as the output
> fifo is not ready in the beginning.
>
> The solution is to trigger asrc before dma on i.MX952, and add delay to
> wait output data is generated then start the EDMA for output, otherwise
> the m2m function has noise issues.
>
> So add an option to start ASRC first for M2M before ASRC is enabled on
> i.MX952.
>
> Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
> ---
> sound/soc/fsl/fsl_asrc.c | 23 +++++++++++++++++++++++
> sound/soc/fsl/fsl_asrc.h | 4 ++++
> sound/soc/fsl/fsl_asrc_common.h | 4 ++++
> sound/soc/fsl/fsl_asrc_m2m.c | 8 +++++++-
> 4 files changed, 38 insertions(+), 1 deletion(-)
>
> diff --git a/sound/soc/fsl/fsl_asrc.c b/sound/soc/fsl/fsl_asrc.c
> index 92fb16f7be45..b6d4f1e09e2e 100644
> --- a/sound/soc/fsl/fsl_asrc.c
> +++ b/sound/soc/fsl/fsl_asrc.c
> @@ -1078,6 +1078,27 @@ static unsigned int fsl_asrc_get_output_fifo_size(struct fsl_asrc_pair *pair)
> return val >> ASRFSTi_OUTPUT_FIFO_SHIFT;
> }
>
> +static bool fsl_asrc_m2m_output_ready(struct fsl_asrc_pair *pair)
> +{
> + struct fsl_asrc *asrc = pair->asrc;
> + enum asrc_pair_index index = pair->index;
> + int retry = 1000;
> + u32 val;
> + int ret;
> +
> + /* Check output fifo status if it exceeds the watermark. */
> + ret = regmap_read_poll_timeout(asrc->regmap, REG_ASRFST(index), val,
> + (ASRFSTi_OUTPUT_FIFO_FILL(val) >= ASRC_M2M_OUTPUTFIFO_WML) ||
> + (--retry == 0), 0, USEC_PER_SEC);

are sure need "retry"? there are timeout, which should be equal to 'retry'.

Frank
> +
> + if (ret || !retry) {
> + pair_warn("output is not ready\n");
> + return false;
> + }
> +
> + return true;
> +}
> +
> static int fsl_asrc_m2m_prepare(struct fsl_asrc_pair *pair)
> {
> struct fsl_asrc_pair_priv *pair_priv = pair->private;
> @@ -1275,6 +1296,7 @@ static int fsl_asrc_probe(struct platform_device *pdev)
>
> asrc_priv->soc = of_device_get_match_data(&pdev->dev);
> asrc->use_edma = asrc_priv->soc->use_edma;
> + asrc->start_before_dma = asrc_priv->soc->start_before_dma;
> asrc->get_dma_channel = fsl_asrc_get_dma_channel;
> asrc->request_pair = fsl_asrc_request_pair;
> asrc->release_pair = fsl_asrc_release_pair;
> @@ -1289,6 +1311,7 @@ static int fsl_asrc_probe(struct platform_device *pdev)
> asrc->m2m_get_maxburst = fsl_asrc_m2m_get_maxburst;
> asrc->m2m_pair_resume = fsl_asrc_m2m_pair_resume;
> asrc->m2m_get_cap = fsl_asrc_m2m_get_cap;
> + asrc->m2m_output_ready = fsl_asrc_m2m_output_ready;
>
> if (of_device_is_compatible(np, "fsl,imx35-asrc")) {
> asrc_priv->clk_map[IN] = input_clk_map_imx35;
> diff --git a/sound/soc/fsl/fsl_asrc.h b/sound/soc/fsl/fsl_asrc.h
> index 1c492eb237f5..60b6865ca952 100644
> --- a/sound/soc/fsl/fsl_asrc.h
> +++ b/sound/soc/fsl/fsl_asrc.h
> @@ -257,6 +257,8 @@
> #define ASRFSTi_OUTPUT_FIFO_WIDTH 7
> #define ASRFSTi_OUTPUT_FIFO_SHIFT 12
> #define ASRFSTi_OUTPUT_FIFO_MASK (((1 << ASRFSTi_OUTPUT_FIFO_WIDTH) - 1) << ASRFSTi_OUTPUT_FIFO_SHIFT)
> +#define ASRFSTi_OUTPUT_FIFO_FILL(v) \
> + (((v) & ASRFSTi_OUTPUT_FIFO_MASK) >> ASRFSTi_OUTPUT_FIFO_SHIFT)
> #define ASRFSTi_IAEi_SHIFT 11
> #define ASRFSTi_IAEi_MASK (1 << ASRFSTi_IAEi_SHIFT)
> #define ASRFSTi_IAEi (1 << ASRFSTi_IAEi_SHIFT)
> @@ -432,10 +434,12 @@ struct dma_block {
> *
> * @use_edma: using edma as dma device or not
> * @channel_bits: width of ASRCNCR register for each pair
> + * @start_before_dma: start asrc before dma
> */
> struct fsl_asrc_soc_data {
> bool use_edma;
> unsigned int channel_bits;
> + bool start_before_dma;
> };
>
> /**
> diff --git a/sound/soc/fsl/fsl_asrc_common.h b/sound/soc/fsl/fsl_asrc_common.h
> index 0cd595b0f629..c8a1a2b5915d 100644
> --- a/sound/soc/fsl/fsl_asrc_common.h
> +++ b/sound/soc/fsl/fsl_asrc_common.h
> @@ -107,6 +107,7 @@ struct fsl_asrc_pair {
> * @asrc_rate: default sample rate for ASoC Back-Ends
> * @asrc_format: default sample format for ASoC Back-Ends
> * @use_edma: edma is used
> + * @start_before_dma: start asrc before dma
> * @get_dma_channel: function pointer
> * @request_pair: function pointer
> * @release_pair: function pointer
> @@ -116,6 +117,7 @@ struct fsl_asrc_pair {
> * @m2m_start: function pointer
> * @m2m_unprepare: function pointer
> * @m2m_stop: function pointer
> + * @m2m_output_ready: function pointer, check output fifo ready or not
> * @m2m_calc_out_len: function pointer
> * @m2m_get_maxburst: function pointer
> * @m2m_pair_suspend: function pointer
> @@ -143,6 +145,7 @@ struct fsl_asrc {
> int asrc_rate;
> snd_pcm_format_t asrc_format;
> bool use_edma;
> + bool start_before_dma;
>
> struct dma_chan *(*get_dma_channel)(struct fsl_asrc_pair *pair, bool dir);
> int (*request_pair)(int channels, struct fsl_asrc_pair *pair);
> @@ -154,6 +157,7 @@ struct fsl_asrc {
> int (*m2m_start)(struct fsl_asrc_pair *pair);
> int (*m2m_unprepare)(struct fsl_asrc_pair *pair);
> int (*m2m_stop)(struct fsl_asrc_pair *pair);
> + bool (*m2m_output_ready)(struct fsl_asrc_pair *pair);
>
> int (*m2m_calc_out_len)(struct fsl_asrc_pair *pair, int input_buffer_length);
> int (*m2m_get_maxburst)(u8 dir, struct fsl_asrc_pair *pair);
> diff --git a/sound/soc/fsl/fsl_asrc_m2m.c b/sound/soc/fsl/fsl_asrc_m2m.c
> index f46881f71e43..77999526dd9e 100644
> --- a/sound/soc/fsl/fsl_asrc_m2m.c
> +++ b/sound/soc/fsl/fsl_asrc_m2m.c
> @@ -253,15 +253,21 @@ static int asrc_m2m_device_run(struct fsl_asrc_pair *pair, struct snd_compr_task
> reinit_completion(&pair->complete[IN]);
> reinit_completion(&pair->complete[OUT]);
>
> + if (asrc->start_before_dma)
> + asrc->m2m_start(pair);
> +
> /* Submit DMA request */
> dmaengine_submit(pair->desc[IN]);
> dma_async_issue_pending(pair->desc[IN]->chan);
> if (out_dma_len > 0) {
> + if (asrc->start_before_dma && asrc->m2m_output_ready)
> + asrc->m2m_output_ready(pair);
> dmaengine_submit(pair->desc[OUT]);
> dma_async_issue_pending(pair->desc[OUT]->chan);
> }
>
> - asrc->m2m_start(pair);
> + if (!asrc->start_before_dma)
> + asrc->m2m_start(pair);
>
> if (!wait_for_completion_interruptible_timeout(&pair->complete[IN], 10 * HZ)) {
> dev_err(dev, "out DMA task timeout\n");
> --
> 2.34.1
>